package com.summli.basic.class08;

import java.util.ArrayList;

/**
 *给定一棵二叉树的头节点head，
 * 返回这颗二叉树中最大的二叉搜索子树的头节点
 */
public class Code05_MaxSubBSTHead {

    public static class Node {
        public int value;
        public Node left;
        public Node right;

        public Node(int data) {
            this.value = data;
        }
    }

    public static Node maxSubBSTHead2(Node head){
        if(head == null){
            return null;
        }
        return process(head).maxSubBSTHead;
    }

    private static Info process(Node head) {
        if(head == null){
            return null;
        }
        Info leftInfo = process(head.left);
        Info rightInfo = process(head.right);
        Node maxSubBSTHead = null;
        int maxSubBSTSize = 0;
        int min = head.value;
        int max = head.value;
        if(leftInfo != null){
            min = Math.min(min, leftInfo.min);
            max = Math.max(max, leftInfo.max);
            maxSubBSTSize = leftInfo.maxSubBSTSize;
            maxSubBSTHead = leftInfo.maxSubBSTHead;
        }
        if(rightInfo != null){
            min = Math.min(min, rightInfo.min);
            max = Math.max(max, rightInfo.max);
            if(rightInfo.maxSubBSTSize > maxSubBSTSize){
                maxSubBSTSize = rightInfo.maxSubBSTSize;
                maxSubBSTHead = rightInfo.maxSubBSTHead;
            }
        }
        //当前层是否是二叉搜索树
        if((leftInfo==null || (leftInfo.max<head.value&&leftInfo.maxSubBSTHead == head.left)) &&
                (rightInfo==null || (rightInfo.min>head.value&&rightInfo.maxSubBSTHead == head.right))){
            maxSubBSTSize = (leftInfo==null?0:leftInfo.maxSubBSTSize) +
                    (rightInfo==null?0:rightInfo.maxSubBSTSize)+1;
            maxSubBSTHead = head;
        }
        return new Info(maxSubBSTHead,maxSubBSTSize,min,max);
    }

    public static class Info {
        public Node maxSubBSTHead;
        public int maxSubBSTSize;
        public int min;
        public int max;

        public Info(Node h, int size, int mi, int ma) {
            maxSubBSTHead = h;
            maxSubBSTSize = size;
            min = mi;
            max = ma;
        }
    }

    // for test
    public static Node generateRandomBST(int maxLevel, int maxValue) {
        return generate(1, maxLevel, maxValue);
    }

    // for test
    public static Node generate(int level, int maxLevel, int maxValue) {
        if (level > maxLevel || Math.random() < 0.5) {
            return null;
        }
        Node head = new Node((int) (Math.random() * maxValue));
        head.left = generate(level + 1, maxLevel, maxValue);
        head.right = generate(level + 1, maxLevel, maxValue);
        return head;
    }

    public static void main(String[] args) {
        int maxLevel = 4;
        int maxValue = 100;
        int testTimes = 1000000;
        for (int i = 0; i < testTimes; i++) {
            Node head = generateRandomBST(maxLevel, maxValue);
            if (maxSubBSTHead1(head) != maxSubBSTHead2(head)) {
                System.out.println("Oops!");
            }
        }
        System.out.println("finish!");
    }

    public static int getBSTSize(Node head) {
        if (head == null) {
            return 0;
        }
        ArrayList<Node> arr = new ArrayList<>();
        in(head, arr);
        for (int i = 1; i < arr.size(); i++) {
            if (arr.get(i).value <= arr.get(i - 1).value) {
                return 0;
            }
        }
        return arr.size();
    }

    public static void in(Node head, ArrayList<Node> arr) {
        if (head == null) {
            return;
        }
        in(head.left, arr);
        arr.add(head);
        in(head.right, arr);
    }

    public static Node maxSubBSTHead1(Node head) {
        if (head == null) {
            return null;
        }
        if (getBSTSize(head) != 0) {
            return head;
        }
        Node leftAns = maxSubBSTHead1(head.left);
        Node rightAns = maxSubBSTHead1(head.right);
        return getBSTSize(leftAns) >= getBSTSize(rightAns) ? leftAns : rightAns;
    }
}
